1. Field of the Invention
The present invention relates to a congestion control system, a service edge node, a guidance server, a congestion control method, a congestion control program, and a program recording medium, and more particularly, to a congestion control system, a service edge node, a guidance server, a congestion control method, a congestion control program, and a program recording medium which are applied to an IP network.
2. Description of the Related Art
In recent years, as described in the disclosure of JP 2005-269197 A titled “INTERNET PROTOCOL TELEPHONY SYSTEM AND CONTROL METHOD FOR INTERNET PROTOCOL TELEPHONY SYSTEM”, significant improvements in sound quality are provided even to a communication mode of using an IP packet for transmission/reception of sound information. Under such circumstances, as a telephone network, an IP telephone service network (service network on an IP network) is rapidly becoming widespread in place of the conventional public switching telephone network (PSTN).
However, as distinct from the conventional telephone network based on a telephone switchboard (PSTN), most of IP telephony networks generally have a configuration in which devices, namely, call control servers, for accommodating subscribers are not distributed in different locations, but concentrated in one location or at most several locations. In addition, one call control server accommodates far more subscribers than one conventional telephone switchboard, and there coexist information items on subscribers in various areas within a single call control server. Therefore, if a failure such as a congestion occurs, an influence thereof is exerted across a wide range of areas.
In other words, in the IP telephony network, devices that exchange control signals for IP telephones such as the call control servers for accommodating subscribers are disposed concentratedly. If a large amount of IP telephone calls occur, much traffic is concentrated on the call control server or the like accommodating subscribers in a wide range of areas, which causes a congested state in the call control server or the like, thereby leading to a state where the IP telephone call is hard to be connected or cannot be connected at all.
In addition, a guidance server, namely, a guiding device, for providing subscribers with various guidance services such as a voice guidance operates in cooperation with the call control server for accommodating subscribers. Therefore, if the call control server falls into such a congested state as to fail in processing of a call initiation request from a subscriber, the guiding device cannot in turn provide a guidance service relating to the occurrence of the congested state.
As a result, the subscriber knows nothing about what is happening, and repeatedly reinitiates the IP telephone call, which accelerates the congested state. Accordingly, the congestion spreads across the entire IP telephony network, and the congested state continues almost without end, resulting in such a critical situation that considerable time is required for a recovery.